In general, it is common knowledge that the reduction of the clearance between the tip of a fan blade and the shroud in which the fan rotates will increase efficiency of the cooling system. Many attempts have been made to minimize the clearance between the tip of the fan blades and the shroud. The latest attempts to reduce the clearance has resulted in the shroud being attached to the tip of the fan blades and the shroud being rotated with the fan. An example of such an arrangement is shown in U.S. Pat. No. 4,566,852 issued to Kurt Hauser on Jan. 28, 1986. The patent discloses an axial fan arrangement in which an attempt has been made to reduce noise level without impairing fan efficiency. An air guide structure is provided which widens in the flow direction starting from adjacent the air inlet edges of the fan blades. The contour of the air guide structure conforms to the facing contour of the fan blades.
U.S. Pat. No. 4,213,426 issued to Richard E. Longhouse on Jul. 22, 1980 discloses an engine cooling fan shrouding comprised of a flexible shroud mounted on a stationary component and a rotating shroud carried by the blade tips of an engine mounted cooling fan.
The combinations disclosed above fail to provide the most efficient combination for reducing noise, preserving longevity and serviceability, and cooling of the engine. For example, movement of the engine relative to the seal will cause rubbing, deterioration of the seal and result in increased clearance, noise and recirculation of the cooling air which reduces the flow of cooling air through the blade. Other fan and shroud assemblies fail to insure a uniform transition of the cooling air going into and coming off of the tip of the blades, resulting in reduced efficiency and increased noise. Other fan and shroud assemblies fail to provide an appropriate outlet path for the cooling air which result in the air flow separation, blade stall, reduced efficiency and increased noise.